In a data network (at least) two parties are involved: the user who wants to transport data and the service provider who is responsible for transporting the data towards the intended destination. In many cases a Service Level Agreement (SLA) between the user and the service provider specifies to what extent the user can use the network of the service provider. To protect the network of the service provider and to allow for fair sharing of the network resources between different users, it is common practice to mention a Peak Information Rate (PIR) in this SLA. The user is only allowed to send data at a rate up to this PIR.
A method and device for implementing such a policy are known from Kowalk, W; Lehnert, R. “The ‘policing function’ to control user access in ATM networks-definition and implementation-”, International Symposium on Subscriber Loops and Services, IEEE September 1988 p. 240–245.
In this ‘Kowalk’ article, a method is described whereby the entrance of a switching device used in an ATM network is monitored for each separate source or user. If a source specific incoming data rate exceeds a predetermined data rate, the incoming data packets are discarded and the incoming data packets are transmitted through the switching device only if the source specific incoming data rate is below the predetermined data rate. Incoming data packets are also eliminated if the switching device becomes congested, that is if the incoming data flow (the total added source specific incoming data rates) exceeds the transport capacity of the switching device.
This is disadvantageous because in case of congestion of the switching device or if the source specific incoming data rate exceeds the predetermined data rate, source specific incoming data is eliminated and thereby lost. This causes errors in the sent data.